This invention relates to heating apparatus comprising a plastics body and a planar heating element, and is particularly directed to the method of attaching the heating element to the body. The invention relates particularly, but not exclusively, to water heating apparatus such as electric kettles.
Various liquid heating appliances have been developed incorporating planar heating elements, and different techniques have been employed for the attachment of the heating element to the body of the heating apparatus. A seal is conventionally provided between the body of the heating apparatus and the heating element, and the attachment methods attempt to ensure a uniform compression of the seal in order to provide reliable sealing.
GB 2,291,325 discloses a method of attaching a planar heating element to a vessel body, which relies upon deformation of the vessel body around the heating element, so as to clamp the heating element in position while compressing a seal. One problem with this approach is that the deformation of the vessel body, which is achieved by heating the body and subsequently applying a force to the material, incurs structural weakness in the material. In the case of a plastics vessel body, subsequent creepage may occur reducing the compression held on the seal. Furthermore, the plastics deformation stage may not be controlled with sufficient accuracy to provide a known uniform level of compression of the seal.